Extraoral force-applying orthodontic appliance

ABSTRACT

An extraoral force-reaction device engageable with the wearer&#39;s head and/or neck, such as a headcap or a neckband, is connected to an intraoral force-applying device, such as molar bands, by force-producing means, such as springs. Snapback of the force-applying means is restricted by limiting the normal range of movement of the force-applying elements and such snapback is controlled in response to relative movement of the intraoral means and the extraoral force-reaction means away from each other beyond a predetermined maximum limit, or in response to stressing of the force producing means beyond a predetermined maximum degree of force exerted by the force producing means. Snapback control may be effected by latching of a limit latch to prevent or limit return movement of the force-reaction device and the force-applying device, or disconnectible means can be disconnected to interrupt the application of primary force to the intraoral means and reaction force to the head or neck engageable means. The force to be exerted by the spring force producing means can be readily adjustable in predetermined increments, such as by engagement of different holes in a spring anchor strap with an anchor pin, or by a linear ratchet device. Also, various components of the extraoral force-reaction device can be assembled and adjusted as to length by connection of separable connections, which may include linear ratchet means.

This application is a continuation-in-part of my application Ser. No.613,243, filed Sept. 15, 1975, for Extraoral Force-Applying OrthodonticApplicance and now abandoned.

BACKGROUND OF THE INVENTION

1. field of the Invention

This application relates to orthodontic appliances capable of applying aprimary force to a jaw, the reaction from which force is applied to theexterior of the head and/or neck by an extraoral force-reaction device.

2. Prior Art

A device for applying primary force to a jaw by an intraoral device andexerting the reaction force on an extraoral force-reaction deviceengageable with the wearer's head or neck is shown, for example, in theArmstrong U.S. Pat. No. 3,526,035. The appliance of the presentinvention constitutes an improvement over the apparatus shown in thatpatent.

The Problem

The problem which has not been solved by prior orthodontic devices hasbeen provision of protection against injury by snapback of the intraoraldevice should the intraoral device be pulled from the patient's mouthand released while it is still connected to the force-producing unit, oreven if the tips of such device were merely disengaged from their toothband sockets and the device then released while such tips are still inthe mouth. Such snapback could occur by a patient improperly removingthe device, or by childish pranks, or by a part of the headgear beingcaught by either a stationary or a moving object. Even if the tips ofsuch device were not pulled from the tooth band sockets a yank on theheadgear resulting from such catching would cause discomfort andpossible injury.

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide effectivecontrol over the snapback of a force-producing unit applying a sustainedyieldable force to a jaw such as by intraoral gear used in orthodontictreatment. More specifically, it is an object to exercise such snapbackcontrol when extraoral force-reaction gear engageable with the wearer'shead and/or neck and force-applying gear are separated more than apredetermined amount, or a force is exerted between such gear componentsof more than a predetermined magnitude.

A further object is to provide such control over the force-producingmeans without appreciably restricting the excursions of which the lowerjaw and head are capable.

If normal corrective force-applying operation of the gear is interruptedby control action on the force-producing unit, it is an object to enablethe gear to be rearranged or restored to its operative condition quicklyand easily.

Another object is to provide in an orthodontic appliance havingextraoral force-reaction and intraoral force-applying components aforce-producing unit which will produce a sustained, substantiallyconstant, predetermined force on a jaw, such as by a preliminarilystressed spring, which force-producing unit can be adjusted quickly andeasily to produce different predetermined degrees of force over a widerange while having a comparatively restricted range of movement for anyselected predetermined force.

An additional object is to provide an orthodontic headgear applianceincluding separate components that can be assembled readily andcomponents of which can be selected to fit patients having heads ofdifferent size.

It is a particular object to provide a disconnectible connection betweenextraoral force-reaction gear and intraoral force-applying gear which isvery precise and which will be disconnected immediately if apredetermined force which it is set to withstand is exceeded onlyslightly, and which gear components can be disconnected by a smallamount of relative movement. Such disconnection will occur whenever theextraoral force-reaction gear is pulled excessively, whetherintentionally or inadvertently, or is merely caught and the wearerexerts the force exceeding the predetermined force.

It is also an object to provide orthodontic gear having the foregoingcapabilities which is light, compact, durable, of simple and economicalconstruction and which can be fitted quickly, easily and accurately tothe patient.

The foregoing objects can be accomplished by orthodontic gear includingintraoral force-applying and extraoral force-reaction componentsconnected by a component connector including a force-producing componentwhich normally is yieldable relative to either the intraoralforce-applying component or the extraoral force-reaction component butwhich has a restricted range of operating movement, and which can eitherbe immobilized relative to the intraoral component or the extraoralcomponent, or freed from the intraoral component or the extraoralcomponent, such as by disconnection, so that the force-producing unitcannot snap back to produce sudden and violent relative contraction ofthe intraoral component and the extraoral component.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2, 3 and 4 are side elevations of a patient shown wearingdifferent types of orthodontic appliances to which the present inventionpertains.

FIG. 5 is a side elevation of a repesentative component connector ofheadgear shown in FIGS. 1, 2 and 3, on an enlarged scale, and havingparts broken away. FIG. 6 is a longitudinal section through suchcomponent connector, shown connected to intraoral force-applying gear.FIG. 7 is a longitudinal section through a portion of the componentconnector on a further enlarged scale.

FIGS. 8, 9 and 10 correspond respectively to FIGS. 5, 6 and 7, but showparts in different relationship.

FIGS. 11 and 12 are longitudinal sections corresponding to FIGS. 6 and7, respectively, and to FIGS. 9 and 10, respectively, but show parts ofthe component connector in another relationship. FIG. 13 is alongitudinal section corresponding to FIGS. 7, 10 and 12 with the partsin still another relationship. FIG. 14 is a longitudinal sectioncorresponding to FIGS. 6, 9 and 11, but shows portions of the connectorin still a different relationship.

FIG. 15 is a longitudinal section through the component connector shownin FIGS. 5 to 14, inclusive, with the various parts in explodedrelationship. FIGS. 16, 17, 18 and 19 are longitudinal sections througha portion of the component connector illustrated in FIGS. 5 to 15,inclusive, illustrating progressive stages in the assembly of the partsshown separated in FIG. 15.

FIG. 20 is a longitudinal section through a portion of a componentconnector corresponding to FIG. 19, but modified to provide a longerstroke of the parts, the construction of FIG. 19 being more suitable forutilization with a headcap such as shown in FIGS. 2 and 3, and theconnector of FIG. 20 being more suitable for combination with a neckbandsuch as shown in FIGS. 1 and 3.

FIG. 21 is a top perspective of a component connector of the samegeneral type as shown in FIGS. 5 to 19, inclusive, but having a slightlymodified construction. FIG. 22 is a top perspective of the componentconnector shown in FIG. 21, with parts in exploded relationship.

FIG. 23 is a fragmentary top perspective of a component connectorshowing an alternative type of construction. FIG. 24 is a topperspective corresponding to FIG. 23, showing another alternative typeof construction.

FIG. 25 is a top perspective of a component connector with parts brokenaway, showing a modification of the construction of FIG. 21. FIG. 26 isa top perspective of the component connector shown in FIG. 25, buthaving the parts in exploded relationship. FIG. 27 is a fragmentary topperspective of the component connector of FIGS. 25 and 26, showing partsin a different relationship.

FIG. 28 is an enlarged top perspective of a fragment of the componentconnector shown in FIGS. 25, 26 and 27, showing details of construction.FIG. 29 is a top perspective of the same structure as shown in FIG. 28,but with parts in a different relationship.

FIG. 30 is a longitudinal section through a fragment of a componentconnector corresponding to the connector fragment shown in FIG. 28, butof modified construction.

FIG. 31 is a longitudinal section through a fragment of a componentconnector corresponding to the fragment shown in FIG. 28 and FIG. 30,but illustrating a further modified type of construction.

FIG. 32 is a longitudinal section, FIGS. 33 and 34 are top perspectives,and FIG. 35 is a longitudinal section of different detailedmodifications of portions of a component connector.

FIG. 36 and FIG. 37 are side elevations of a fragment of a componentconnector, showing parts in different relationships, and FIG. 38 is atop perspective of the same fragment of a component connector with partsin still a different relationship.

FIG. 39 is a side elevation, and FIGS. 40, 41, 42 and 43 arelongitudinal sections through a portion of a component connector ofanother type, the several figures showing parts in differentrelationships. FIG. 44 is a transverse section taken on line 44--44 ofFIG. 41. FIG. 45 is a top perspective of the same portion of thecomponent connector showing the parts in exploded relationship.

FIG. 46 is a side elevation of a different type of component connector,certain features of which are similar to corresponding features of thecomponent connector shown in FIGS. 25 and 26; FIG. 47 is a longitudinalsection through such connector; and FIG. 48 is a transverse sectiontaken on line 48--48 of FIG. 47.

FIG. 49 is an edge elevation of a modification of the type of componentconnector shown in FIGS. 46, 47 and 48.

FIG. 50 is a side elevation of a component connector abutting adifferent type of force-producing element, and having parts broken away.FIG. 51 is a longitudinal section through such connector.

FIG. 52 is a side elevation of a component connector having still adifferent type of force-producing member, parts being broken away.

FIG. 53 is a plan of a preferred type of component connector with partsbroken away,

FIG. 54 is a top perspective of such a connector, and

FIGS. 55, 56 and 57 are plans of such connector with parts broken away,such views showing parts of the connector in progressively differentrelationships.

FIG. 58 is an edge view of a component of the connectors shown in FIGS.53 to 57 inclusive.

DETAILED DESCRIPTION

While orthodontic gear including an extraoral force-reaction componentengageable with the wearer's head and/or neck and a force-applyingcomponent, such as an intraoral component, of various types have beenused, representative types of gear are illustrated in FIGS. 1, 2 and 3.In each instance the gear includes two or three principal components,namely a force-applying component, by which a force is applied to a jaw,and an extraoral force-reaction band component, by which a reactionforce is applied to the head and/or neck, and one or two componentconnectors which usually include a force-producing unit for producing asustained force applied to the force-applying component. The term"intraoral" as used in the following description and claims is intendedto include force-applying devices for orthodontic treatment whichcontact the exterior of the lower jaw, such as a chin cup.

In FIG. 1 the extraoral force-reaction component includes a neckband 1,a tie rod 2 connected to the intraoral component, and a force-producingconnector unit 3. In FIG. 2 the extraoral force-reaction gear includesthe headcap 4 composed of a lower band 4a extending around the back ofthe head and an upper band 4b extending across the top of the head. Theends of these bands are connected together and to the rearward end ofthe force-producing connector unit 3. In FIG. 3 the neckband 1 and theheadcap 4 have individual force-producing connector units 3 which may beof the same type, and both of which are connected to the tie rod 2.

The force produced by the force-producing unit 3 in each instanceapplies a pull on the tie rod 2, which exerts a corresponding rearwardforce on the intraoral, or force-applying component of the headgear towhich the tie rod 2 is connected. It is evident that the pull producedby the neckband type of gear shown in FIG. 1 is downward and rearwardfrom the mouth, whereas the pull produced on tie rod 2 by the headcaptype of extraoral gear shown in FIG. 2 is upward and rearward from themouth. By utilizing a combination of the neckstrap and the headcap asshown in FIG. 3, and arranging for the headcap force-producing connectorunit and the neckband force-producing connector unit to producepredetermined forces of desired magnitude, the direction as well as thedegree of pull exerted on the tie rod 2 can be selected over aconsiderable range.

FIG. 4 illustrates diagrammatically various vectors representingdifferent directions in which the pull on the tie rod 2 can be exertedby appropriately adjusting or setting the force-producingcharacteristics of the neckband and headcap force-producing units 3 andthe lengths of connections between such force-producing units and thetie rod. If the headcap force-producing unit is adjusted to produce onlya small force, the pull will be produced primarily by the neckbandforce-producing unit 3, so that the pull applied to the tie rod 2 willbe primarily along the vector Fa. Alternatively, if the force-producingunit 3 of the neckband is adjusted to produce little or no force, thepull on the tie rod 2 will be exerted almost entirely by the headcapforce-producing unit 3 and will act generally along the vector Fb. Ifthe forces produced by the neckband force-producing unit 3 and the forceproduced by the headcap force-producing unit 3 are approximately equal,the resulting pull on the connector component 2 will be along a vectorFc approximately bisecting the angle between the force lines Fa and Fbextending through the neckband force-producing unit and the headcapforce-producing unit, respectively.

By increasing the force produced by the neckband force-producing unit 3somewhat and/or decreasing the force produced by the headcapforce-producing unit 3 somewhat, the direction of pull on the tie rod 2can be lowered, such as to the vector Fd. Alternatively, if the headcapforce-producing unit 3 is arranged to provide an increased force and/orthe neckband force-producing unit 3 is arranged to provide a reducedforce, the direction of pull on tie rod 2 can be raised somewhat, suchas to the line of vector Fe. If the force produced by the neckbandforce-producing unit 3 is increased to a greater extent and/or the forceproduced by the headcap force-producing unit 3 is reduced farther fromequality, the vector of the pull on tie rod 2 can be lowered from themedian vector Fc below the vector Fd, such as to the vector Ff.Alternatively, the headcap force-producing unit 3 can be arranged toproduce a considerably greater force and/or the neckband force-producingunit 3 can be arranged to produce a considerably smaller force, so thatthe vector of the pull on tie rod 2 can be raised from the median vectorFc beyond the location of the vector Fe, such as to the location of thevector Fg.

In order to be able to arrange the pull on the tie rod 2 in differentdegrees and in different directions as discussed above, it is desirablefor the force-producing units to be constructed for easy substitution inthe gear or for easy adjustment to produce different degrees of force.Also it is important that the gear be designed so that snapback of theforce-producing unit can be controlled reliably to avoid sudden orviolent return contraction of the component applying the reaction forceto the head or neck and the component through which the force is appliedto the wearer's jaw. As an additional feature it is desirable to enablethe various components of the headgear to be connected readily anddisconnected at will or automatically in response to relativedisplacement of components more than a predetermined amount.

The principal features of the invention can be incorporated in aconnector which connects an extraoral force-reaction band member, suchas a neckband 1 or a headcap band structure 4a, 4b, with a tie rod 2, bywhich the pulling force is applied to intraoral force-applying gear.FIGS. 5 to 18 show one type of connector. Such connector includes aforce-producing unit 3 having a backing 5 that can be attached suitablyto the reaction force band component by being bonded or stapled to suchcomponent, as illustrated generally in FIGS. 1, 2, 3 and 4, and by thedot-dash line illustration of band means 4 in FIGS. 6, 9 and 14.Preferably the force-producing means carried by the backing 5 isenclosed in a housing tube 6. In the force-producing unit of FIGS. 5 to19, the force-producing means is shown as a helical tension spring 7,slidable within the tube 6. The force-producing unit can be connected tothe tie rod 2 by a side strap 8, having apertures 9 at regularly spacedintervals along its length for engagement by a hook on the end of thetie rod. The purpose of having a plurality of apertures in the strap isto enable the tie rod hook to be engaged in the appropriate aperture sothat the proper length of connection between the force-producing unitand the tie rod for the particular patient can be selected.

Instead of the strap 8 being connected directly to the spring 7, it ispreferred that an intermediate strap 10 be interposed between the strap8 and the spring. The end of such intermediate strap adjacent to thespring is connected to a hook on the end of the spring by a connectinghook 11 preferably made of resilient strip metal or plastic. The shankof such hook is apertured to engage the spring and hook. Thereversely-bent end of hook 11 passes through a slot in the end of theintermediate strap 10.

The hook 11 serves not only to connect the end of intermediate strap 10to the adjacent end of spring 11, but such hook can serve the additionalpurpose of controlling snapback of the spring under certain conditions.During normal use of the appliance, as illustrated in FIG. 6, theintermediate strap extends beneath a bridge 12 upstanding from andintegral with the backing 5, which preferably is of molded plasticmaterial. As the strap 8 and intermediate strap 10 are pulled to theright relative to the backing 5 from the normal operating position shownin FIG. 6, the hook 11 will be pulled toward the bridge 12 until anupwardly bowed leaf part 13a of the return portion of the hook 11 isengaged with the bridge, as shown in FIG. 9.

The hook 11 is sufficiently flexible so that the upwardly bowed portion13a can be depressed to enable that portion of the hook to be pulledbeneath the bridge from the position of FIG. 9 to the position of FIG.10. In order to contract the spring hook to this extent, it is necessarythat the pull on the spring exceed the normal operating pull. Theoperating pull could, for example, be as much as thirty-two ounces andthe pull required to slide the hook from the position of FIG. 9 to theposition of FIG. 10 could be four or five pounds, for example. Theamount of pull required would depend upon the relative heights of thebridge 12 and the hook 11 and the flexibility characteristics of thehook and of the bridge.

When the hook 11 has reached the condition of FIG. 10, very littleadditional pull is required to slide the upward bulge 13a of the hook tothe right beyond the bridge to the position of FIGS. 11 and 12. When thehook has reached this position, if the pull on the strap 8 andintermediate strap 10 is relieved, the pulling force of spring 7 will beinsufficient to pull the hook back under the bridge 12. Consequently,the hook 11 will constitute a limit latch which, in the latched positionof FIGS. 11 and 12, will control the snapback of spring 7 byimmobilizing the spring to prevent contraction movement of the springfrom the position of FIG. 11, through the position of FIG. 10, to thecondition of FIG. 6.

The limit latch 12, 13a will be engaged whenever the pull on tie rod 2is sufficient to move the bow 13a of spring 11 under the bridge 12 tothe position of FIG. 11. To effect such movement, the tie rod 2 musthave been moved relative to the force-producing unit 3 and the head orneck engaging band means beyond a predetermined distance. In order toeffect such relative movement between the tie rod and theforce-producing unit and band means, it will be necessary to apply aseparating force between the tie rod and the force-producing unitexceeding a predetermined value. Consequently the parts can beproportioned and spaced so that the limit latch will be latchedautomatically in response to predetermined relative displacement of thetie rod 2 and backing 5.

Moreover, the flexibility characteristics of the material of the hook11, the width and thickness of the hook strip material, the hookproportions, and the height of the bow 13 with respect to the height ofthe bridge 12 can be selected so that the bow of the hook will be movedfrom the position of FIG. 9, through the position of FIG. 10, to theposition of FIG. 11 automatically in response to exertion of apredetermined degree of separation force between the intermediate strap10 and the backing 5. While the force exerted by spring 7 on the hook 11in the position of FIG. 11 will be insufficient to move the hook back tothe left under the bridge 12, the bow 13a can be depressed sufficientlyby manual pressure applied to it so that the pull of spring 7,especially if aided somewhat by manual pushing, or in some instancesmanual pushing alone, will move the hook back under the bridge to theposition of FIG. 10, whereupon the spring can return the hook to theposition of FIGS. 6 and 7.

It is preferred that the backing 5 have a further bridge 14 at the sideof bridge 12 remote from spring 7. Such bridge is lower than bridge 12so that, while the hook 11 can pass under bridge 12, it cannot pass tothe right, as seen in FIGS. 11, 12 and 13, beneath bridge 14. To insurea positive stop between the intermediate strap 10 and the bridge 14, theleft end of such strap can be provided with abutments 15 projection fromthe intermediate strap on opposite sides of hook 11 far enough to engagethe left side of bridge 14 positively, as shown in FIG. 13.

During movement of the hook 11 from the position of FIG. 6 to theposition of FIG. 9, the hook may tend to drag along the housing tube 6and to drag a portion of spring 7 along such tube. To preventappreciable lengthwise movement of the tube as a result of such draggingaction, a stop projection 16 can be provided upstanding from the backing5 for engagement by the tube end to limit its movement toward bridge 12.

While the limit latch 12, 13a will immobilize the spring 7 in thecondition of its maximum extension permitted by movement of theintermediate strap 10, the reaction force resisting band means 1 or 4will still be connected to the tie rod 2 by the force-producing unit 3.A pulling force might be exerted on the intraoral component of theappliance sufficient to deform a portion of the appliance inadvertentlyby application of a strong force to it. Consequently, it is desirablefor the tie rod 2 and the head or neck engaging force reaction bandmeans, such as the neckband 1 or the headcap 4, to be disconnectedautomatically in response to application of a pulling force to the tierod exceeding a value higher than the amount of pull required to latchthe limit latch mechanism. The degree of pull to disconnect the tie rodmight, for example, be seven pounds.

Disconnection between the tie rod 2 and the neckband or headcappreferably is accomplished by disconnecting the side strap 8 from theforce-producing unit 3. Such a disconnectible connection is shown inFIGS. 5 to 22, inclusive, as including the widened end portion 17 of theintermediate strap 10 remote from the end of such strap carrying theabutments 15. Such widened end portion has a bridge 18, which canreceive beneath it the side strap 8, as shown in FIGS. 8 to 12,inclusive. Spaced to the left of the bridge 18 and upstanding from theintermediate strap 10 is the stop rib 19 having a dual function. Theleft side of such rib is engageable with bridge 14 to limit movement ofthe intermediate strap to the left, and its opposite side is engageableby the adjacent end of the side strap 8 to limit its movement to theleft relative to the intermediate strap 10.

The end portion of the side strap 8 remote from the tie rod 2 carries areturn-bent load-releasing strip spring, preferably of metal. Such stripincludes a return bend 20 hooked through an aperture in the form of aslit in the end portion of the strap 8 and a bowed spring leaf 21projecting outwardly from the strap. The distance between the bridge 18and the rib 19 is sufficiently great to accommodate the major portion ofthe length of the bowed leaf spring strip 21, so that such spring stripwill fit between the bridge 18 and the rib 19, as shown in FIGS. 9, 10,11 and 12, for example.

The flexibility of the bowed spring leaf 21 and the height of the bridge18 are arranged so that the spring can be depressed to the conditionshown in FIG. 13 by application of a pulling force to the tie rod 2 andside strap 8 of a predetermined value, such as the value of seven poundsmentioned above. When the bowed spring leaf has been depressed in thismanner to slide beneath the bridge 18, the side strap 8 can be movedeasily to the right from the position of FIG. 13 to the disconnectedrelationship of FIG. 14. Thus, while the intermediate strap 10 remainsattached to the force-producing unit 3 by the limit latch hook 11 or theabutments 15 and the bridge 14, the side strap 8 and the intermediatestrap 10 will be completely separated to disconnect the tie rod 2 fromthe head-engaging reaction force component such as the neckband 1 or theheadcap 4.

FIGS. 5 to 14, inclusive, illustrative the parts of the force-producingunit 3 and representative intraoral gear in various relative positions.For purposes of illustration the intraoral gear is shown in FIGS. 6, 9,11 and 14 as including the inner bow 2a of a double face bow, the tierod 2 forming the outer bow. The inner tip 2b of the inner bow isreduced, as shown in FIG. 9, for insertion into the socket 2c of a molarband 2d, as shown in FIG. 6. If the face bow is grasped and pulled inthe direction indicated by the arrow at the right of FIG. 9, the tip 2bof the face bow will be pulled out of the molar band socket 2c, whilethe inner bow of the face bow remains in the mouth.

It will be evident that the displacement of the face bow from therelationship to the force-producing unit 3 shown in FIG. 6 to therelationship shown in FIG. 9 is quite small, but is adequate to providefor maximum movement between the force-producing unit and the face bowwhich could be accomplished by tilting of the head. Alternativey, whenthe head is erect or untilted, the face bow can be moved relative to theforce-producing unit to the position of FIG. 9 by grasping the face bowmanually and pulling in the direction indicated by the arrow in FIG. 9.While such manual movement is undesirable, the degree of displacement ofthe face bow from the teeth indicated in FIG. 9 would be insufficient towithdraw the inner face bow from the mouth. If the face bow werereleased, the force exerted on the side strap 8 by the force of spring 7acting on tie rod 2 would snap the double face bow inwardly farther intothe mouth, but the possible range of movement is quite small, i.e. thedistance that stop rib 19 could move to bridge 14, as shown in FIG. 9.Consequently, if inner tips 2b strike soft tissue in the mouth, nosubstantial injury would occur.

Before the face bow could be displaced from the force-producing unit 3sufficiently far to withdraw the inner bow 2a from the mouth, the limitlatch bow spring 13a would have been moved through the position shown inFIG. 10 at least to the position of FIG. 11. By such displacement thelimit latch bow spring 13a would have moved past the bridge 12, asillustrated in FIG. 11, to latched position. If the pull on the face bowwere released at that time, the face bow would not snap back appreciablybecause the latch 12, 13a would have immobilized the spring 7 in thecondition shown in FIG. 11.

If the pulling force on the face bow were continued in the directionindicated by the arrow in FIG. 11, the tie rod 2 would be displacedfurther to pull the intermediate strap 10 from the position of FIGS. 11and 12 to the position of FIG. 13, in which the abutments 15 and/or thelatch bow spring 13a is engaged with the stop bridge 14. Continuedpulling would cause the bridge 18 of the intermediate strap to exert asufficient wedging action on the bowed leaf spring 21 to depress the bowfor movement into the position beneath the bridge 18 shown in FIG. 13.Further continued pulling on the face bow would cause the spring 21 toslide out from under the bridge 18, so that the side strap 8 would bedisconnected from the intermediate strap 10, as indicated in FIG. 14,and the face bow would be freely movable in the direction indicated bythe arrow in FIG. 14 relative to the force-producing unit 3.

Representative values of force to effect latching of the limit latch 12,12a and to effect disconnection of the connection 18, 21 have beenstated. It is also improtant to design the appliance so that the tie rod2 and the force-producing unit 3 are displaced through particulardistances to effect latching the limit latch and disconnection of theseverable connection. It is desirable to enable the tie rod 2 and theforce-producing unit 3 to be moved relatively to a greater extent whenthe force-producing unit is mounted on the neckband 1 than when theforce-producing unit is mounted on a headcap 4 before the limit latchlatches or the disconnectible connection is disconnected.

A typical example for a headcap-mounted force-producing unit 3 wouldenable the tie rod 2 and such force-producing unit to move through adistance within the range of five to eight millimeters before the limitlatch bow 13 comes into contact with the ridge 12 in the position shownin FIGS. 9 and 10. This type of construction is illustrated in FIGS. 5to 18, and particularly in FIG. 19. The parts of the appliance shown inFIG. 20 are the same as the parts of the appliance shown in FIG. 19,except that the length of the backing 5 between tube stop 16 and bridge12 of somewhat greater than the distance between the stop and bridge inFIG. 19, and the length of the intermediate strap 10 between abutments15 and stop rib 19 is correspondingly greater. The extent of normalmovement permitted by the structure shown in FIG. 20 before the bow 13aengages the latch bridge 12 would be twelve to fourteen millimeters, forexample, instead of five to eight millimeters as in the case of aheadcap. The maximum yieldable extension and contraction relativemovement of the strap 10 and force-producing unit should not exceedsixteen millimeters, or a force change of twelve ounces, during suchmovement. The construction shown in FIG. 20 is more suitable forassociation with a neckband 1 to accommodate excursions of the lower jawand the head.

Relative movement of the tie rod 2 and the force-producing unit 3 afterthe latch bow 13a comes into engagement with the latch bridge 12 inorder to secure the latch as shown in FIG. 12, would be the samewhatever normal relative movement of the tie rod and force-producingunit could occur prior to such contact of the latch bow with the latchbridge. The additional extent of relative movement to secure the latchcould be three millimeters, for example. In order to disconnect the sidestrap 8 and the intermediate strap 10 by relative movement of the bowspring 21 and the bridge 8 from the relationship shown in FIGS. 11 and12 to the relationship in which the bow spring has just cleared thebridge 18 beyond the position of FIG. 13, could be an additional fourmillimeters or less.

Thus relative movement of the tie rod 2 and the force-producing unit 3beyond the normal range of movement for a distance of three millimeterswould effect latching of the limit latch to immobilize spring 7 whetheror not a disconnectible connection is included. If the limit latch wereomitted, such as by omitting the bridge 12, the disconnectibleconnection could be disconnected by a movement of four millimeters orless beyond the normal range of movement. If both the limit latch andthe disconnectible connection are utilized, the latching of the limitlatch and the disconnection of the connection would be accomplished byrelative movement of the tie rod and the force-producing unit through adistance of approximately seven millimeters beyond the range of normalrelative movement of the tie rod and the force-producing unit.

It is important for the limit latch to be operated, or for the sidestrap 8 to be disconnected from the force-producing unit 3, or both,before the intraoral component of the orthodonic gear, including theinner bow 2a and the tips 2b, has been withdrawn completely from thewearer's mouth, or ideally before the inner bow tips have been withdrawnfrom the molar band sockets, so that snapback of the face bow caused bythe force-producing unit cannot occur when the inner bow of the doubleface bow is in a position such that snapping-back action of such bowmight cause the inner bow tips 2b to penetrate an external portion ofthe face. Consequently, the normal range of relative movement of theside strap 8 and the force-producing unit 3 must be sufficiently smallso as to initiate latching action of the limit latch to immobilize thespring 7, and/or to effect disconnection of the side strap 8 from theforce-producing unit 3, before the inner bow 2a and tips 2b have beenwithdrawn completely from the mouth of the wearer, such as when theinner bow has not been pulled appreciably farther outward from the mouththan the position of the inner bow shown in FIG. 11.

Both to latch the limit latch and to disconnect the side strap 8 fromthe intermediate strap 10 will, of course, require a greaterdisplacement of the intraoral device from the force-producing unit 3beyond the normal range of movement of these parts. Where a limit latchand a disconnectible connection are arranged in series, therefore, therange of movement of the intraoral device relative to theforce-producing unit should be as small as reasonably possible, whilestill affording sufficient relative movement between the side strap 8and the force-producing unit 3 to enable the hook of the tie rod 2 to beengaged in the appropriate hole 9 of the side strap 8 and to accommodatereasonable excursive motion of the lower jaw relative to the headwithout effecting latching of the limit latch or disconnection betweenthe side strap 8 and the force-producing unit 3.

The strap 10 is shown in FIGS. 5, 6 and 7 in approximately the middle ofits operating range. If pull on the side strap 8 were completelyrelaxed, the force produced by spring 7 would pull the intermediatestrap 10 to the left, as seen in FIGS. 5, 6 and 7, until the stop rib 19is drawn into abutment with the right side of the low bridge 14. Theother extreme of the normal range of relative movement of the tie rod 2and force-producing unit 3 is reached when the bow spring portion 13a ofthe hook 11 is engaged with and starts to be drawn under the bridge 12of the limit latch mechanism.

With the parts of the orthodontic appliance in the normal treatingrelationship of FIGS. 5, 6 and 7, the spring 7 of the force-producingunit would exert a sustained and substantially uniform force on the facebow 2,2a directed inwardly of the mouth. As explained in connection withFIGS. 1 to 4, inclusive, it may be desirable to alter the force appliedto the face bow for treating different orthodontic conditions. While thespring 7 could be preliminarily stressed to produce substantially apredetermined force for application to the intraoral device, so that theforce produced could be altered by selecting different preliminarilystressed springs, the force-producing unit 3 shown in the appliance ofFIGS. 5 to 22 can be adjusted so as to produce different degrees offorce.

To provide for selective adjustment of the spring 7 by increments over aconsiderable range of selectible average treatment forces, the end ofspring 7 remote from the hook 11 is attached to one end of an anchorstrap 22. This anchor strap carries buttress teeth 23 spaced along itslength distances corresponding to increments of force, for which forceincrements the stress of and force produced by spring 7 can be alteredwithout changing appreciably the variation in force which occurs as aresult of relative movement of the tie rod 2 and the force-producingunit 3 during normal use of the gear. The abrupt sides of such teethface the spring so that they can engage an edge of a bridge 24 remotefrom the spring formed by a band having its length extendingtransversely of the anchor strap 22, beneath which bridge the anchorstrap can extend. The end portion of anchor strap 22 remote from spring7 can be confined by tucking it through a keeper slot 25 in the backing5 at the side of the anchor bridge 24 remote from the spring 7.

The buttress-toothed anchor strap 22 and the bridge 24 upstanding fromthe backing 5 constitute a linear ratchet which can be adjusted to alterthe force produced by the spring 7. The end of the anchor strap remotefrom that spring is simply threaded beneath the bridge 24 and pulled sothat successive teeth 23 engage the bridge unitl the spring 7 has beenstressed to the extent necessary for the spring to produce the desireddegree of orthodontic treatment force which is applied to the intraoralcomponent of the appliance. The free end of the anchor strap is thentucked through the slot 25 of the backing 5.

The various parts of the force-producing unit 3 are shown in explodedrelationship in FIGS. 15 and 22. The procedure by which such parts canbe assembled into the force-producing unit shown in FIGS. 5 to 14 isillustrated in FIGS. 16, 17 and 18. The end of intermediate strap 10remote from its bridge 18 is threaded first beneath bridge 14 and thenbeneath bridge 12 carried by the backing 5. The spring-connecting hook11 can then be inserted through the slot in the end of the intermediatestrap, as indicated in broken lines in FIG. 16, and one hook of thespring 7 can be threaded through the aperture of hook 11.

Next the aperture of the anchor strap 22 can be engaged with the hook onthe other end of the spring, and the housing tube 6 can then be slippedlengthwise over the anchor strap and the spring into the position shownin FIG. 17. Next the free end of the anchor strap 22 can be threadedbeneath the anchor bridge 24 and pulled to the left until the selectedtooth 23 of the linear ratchet corresponding to the desired force to beproduced by spring 7 has engaged the left side of the anchor bridge. Thetail of the anchor strap can then be tucked through the keeper slot 25as shown in FIG. 18.

Finally, the end of the side strap 8 remote from the load-releasingspring 20 is threaded beneath the bridge 18 of the intermediate strap 10in the direction indicated by the arrow in FIG. 18. When the left end ofsuch side strap has been seated between the bridge 18 and the stop rib19, as shown in FIG. 6 for example, the hook on the end of the tie rod 2can be engaged in an aperture 9 of such side strap, selected to providethe proper spacing between the neckband 1 or headcap 4 and the intraoralcomponent of the appliance, to enable the force produced by theforce-producing unit to be applied to the desired manner to theintraoral component. Any tag end of the side strap extending forwardlybeyond the aperture 9 in which the hook of the tie rod 2 is engaged canthen be cut off, if desired.

In providing a movement-limiting means, such as a limit latch, and/or adisconnectible connection for the side strap of an orthodonticappliance, consideration should be given to the amount of movement thatshould be afforded for the side strap before the movement-limitingmeans, such as a limit latch, is actuated or the disconnectibleconnection is disconnected, which considerations have been discussedabove. Because of excursions of the head and upper jaw relative to theneck, excursions of the lower jaw relative to the head and excursions ofthe lower jaw relative to the neck, more lengthwise movement of the sidestrap 8 should be permitted before the latch is latched or theconnection is disconnected if the force-producing unit is used inconjunction with a neckband 1 than would be required where theforce-producing unit is used in connection with a headcap 4. Acomparison of the structures shown in FIGS. 19 and 20 indicates thealteration in design which will provide a greater range of normalmovement between the side strap 8 and the force-producing unit 3 for aneckband installation than for a headcap installation.

As has been discussed above, contraction movement of the spring 7 to theleft is limited by engagement of the stop rib 19 on the intermediatestrap 10 with the right side of the low bridge 14. In FIGS. 19 and 20the stop rib 19 is the same distance from the low bridge 14, indicatingthat ormal pull is being applied by the spring 7 through the side strap8 to the tie rod 2. Movement of the intermediate strap 10 to the right,both in the construction of FIG. 19 and in the construction of FIG. 20,is limited by engagement of the limit latch bow spring 13a with the leftside of the bridge 12.

The structure of FIG. 19 is intended for use with a headcap 4, and thestructure of FIG. 20 is intended for use with a neckband 1, because inFIG. 19 the bridge 12 is closer to the tube stop 16 than it is in FIG.20. Consequently, the latch bow spring 13a can move farther to the rightfrom the position shown when the structure of FIG. 20 is used than wherethe structure of FIG. 19 is used. The extent of the normal range ofmovement of the side strap 8 relative to the force-producing unit 3 canbe altered simply by changing the length of the interval betweenabutments 15 and stop rib 19 of the strap 10 and locating bridge 12farther from or closer to the tube stop 16 to alter the position of theadjacent end of spring 7 at opposite ends of the normal range ofmovement of the side strap 8.

While FIG. 9 shows the abutments 15 as passing beneath the crossbar ofthe bridge 12, the central portion of the bridge can be stiffened toreduce its deflection and notches can be provided beneath the oppositeends of the bridge crossbar to permit passage of the abutments 15, asshown in the bridge 12' of FIGS. 21 and 22. The bow spring 13a of thelimit latch would engage the thickened central portion of the bridgecrossbar and be depressed, whereas the abutments 15 spaced transverselyof the intermediate strap 10, as shown best in FIG. 22, would passthrough the downwardly opening notches in the opposite end portions ofthe bridge crossbar but engage bridge 14 to provide a positive stop.With the exception of this modification, the appliance shown in FIGS. 21and 22 is similar to that of FIGS. 5 to 20, inclusive.

FIG. 23 shows an alternative type of keeper arrangement for the tail ofthe spring anchor strap 22. In this instance the anchor strap is held inposition by an upright anchor pin 26 upstanding from the backing 5 andsubstantially straight throughout its length. Such pin is engaged in anaperture 23' selected from one of a row of apertures arranged along thelength of the spring anchor strap corresponding to different selectedforce-producing stresses of the spring 7. The anchor pin can lean tosome extent toward or away from the spring 7, as may be preferred formost convenient engagement of an aperture in the strap with the pin.

At the side of the anchor pin 26 remote from spring 7, arranged inseries relationship, are two or more cantilever bridges 24' mountedalternately at opposite sides of the strap. At the side of the strapopposite the root of each cantilever bridge is a wedge-shaped side stop27 spaced transversely of the backing 5 to some extent from the tip ofthe cantilever bridge. The tip of each bridge has an under bevel on askew angle, inclined toward the spring and the root of the bridge. Suchcombination of side stops and cantilever bridges enables the tail of theanchor strap beyond the anchor pin to be swung to and fro, first towardthe stop 27 nearest the anchor pin 26, next in the opposite directionwhile being slid up the inclined side of such stop and down under thecooperating cantilever bridge 24', and then in the opposite direction tobe slid up the inclined side of the next farther removed stop 27 anddownward to be caught under the cantilever bridge 24' cooperating withthat stop.

While any number of cooperating stops and cantilever bridges could bearranged in series lengthwise of the anchor strap, two such successivestops and cantilever bridges constitute a satisfactory keeper for thetail of the anchor strap. The adjacent end of the housing tube 6 for thespring 7 can be maintained in position centered relative to the keeperstructure by posts 28 upstanding from the backing 5 and spacedtransversely of the tube to receive its end between them as shown inFIG. 23. A particular advantage of this type of construction is that thetail of the anchor strap can be secured in any selected position ofadjustment simply by manipulation with the fingers. By holding the tailof the anchor strap in the proper longitudinally adjusted position as itis slid up the ramp of the first stop 27 and tucked under the firstcantilever bridge 24', the desired aperture 23' can be pressed down overthe anchor pin 26. The portion of the anchor strap tail beyond the firstkeeper element can then be swung farther in the same direction and backto be engaged with the next keeper element.

In the modified keeper construction shown in FIG. 24, a single keeperelement including the combination of a stop 27 and a cantilever bridge24' is combined with a keeper slot 25 through which the end portion ofthe anchor strap tail is tucked after the tail has been initially caughtunder the cantilever bridge 24' of the first keeper element. In thismodification the end of the housing tube 6 is shown as being held downmore positively by a band 29 bridging the end of the tube instead oflateral movement of the tube end being restrained simply by being lodgedbetween posts 28 as shown in FIG. 23.

In the force-producing unit 3 shown in FIGS. 25 and 26, the centralportion of the spring housing tube 6 is confined by a wider band 29'located generally centrally of the backing 5. Such band will deterbuckling of the tube by the force of a stressed spring 7 even if thematerial of the tube is quite flexible. Also in this modification only asingle keeper element including a stop 27 and a cooperating cantileverkeeper bridge 24" is shown. Such cantilever bridge, however, is longerthan the bridges 24' shown in FIGS. 23 and 24, so as to confine the tailof the anchor strap more reliably than would a single keeper element ofthe type shown in FIG. 23.

The connection of the side strap 8 to the force-producing unit 3 shownin FIGS. 25 to 29, inclusive, like that described in connection withFIGS. 5 to 22, has both a limit latch and a disconnectible connection.The disconnectible connection including the bowed spring leaf 21cooperating with the bridge 18 is the same as that described inconnection with the apparatus of FIGS. 5 to 22. FIG. 27 shows how theside strap 8 can be assembled with the intermediate strap 10, as alsoillustrated in FIG. 18.

The limit latch structure shown in FIGS. 25 to 29 differs from the limitlatch structure of FIGS. 5 to 22 in that a molded buttress tooth 13b issubstituted for the bow spring 13a of the limit latch of FIGS. 5 to 22.Preferably the backing 5 and the intermediate strap 10 of the FIGS. 25and 26 are molded of plastic material. The inclined or sloping side ofthe buttress tooth 13b will engage with the left side of the bridge 12".Bridge 12" also serves as a stop for the end of tube 6 as the side strap8 is pulled in the direction indicated by the arrow in FIG. 25. Suchbuttress tooth 13b and/or the bridge 12" will be sufficiently yieldableto enable the buttress tooth to be pulled beneath the bridge when aforce of predetermind maximum value is applied to the side strap 8 andto the force-producing unit 3 tending to separate them.

When the buttress tooth 13b has been pulled beneath the bridge 12" tothe side opposite that shown in FIG. 25, the force of the spring 7 willbe insufficient to pull the abrupt or sheer side of such tooth backunder the bridge. The shoulder 15' of the enlarged end of theintermediate strap 10, with which enlarged end the spring is engaged,will abut the left side of the bridge 12" after the buttress tooth 13bhas passed to the right of such bridge to prevent the intermediate strap10 and the spring 7 from being extended relative to the backing 5 to agreater extent. The buttress tooth 13b can be moved manually at willback under the bridge 12" from the latched position shown in FIG. 28 byswinging the intermediate strap 10 relative to the bridge as shown inFIG. 29. The corners of the buttress tooth 13b are clipped to providewedging chamfers that can be pushed against the right side of the bridgeto wedge it up sufficiently to enable the buttress tooth to move backbeneath the bridge to the position of FIG. 25.

In FIG. 30 a further modification of the limit latch is shown. In thisinstance a bow spring 13c is formed as an integral part of theintermediate strap 10. As in the types of limit latches describedpreviously, a sufficient pull on the intermediate strap to the right, asseen in FIG. 30, will effect a wedging action between the bridge 12" andthe bow spring 13c so that one or both of them will yield sufficientlyto enable the bow spring to pass to the right beneath the bridge 12"into latched position. Abutment of the shoulder 15' of the strap endwith the left side of the bridge will limit extension movement of theintermediate strap and the force-producing unit. To release the limitlatch, the bow 13c can be pressed downward manually and pushed to theleft so that, with the aid of the spring 7, the bow can be moved backbeneath the bridge 12" to the position shown in FIG. 30.

The parts are shown in FIG. 30 at the right end of the normal operatingrange. The left end of the operating range is established by engagementof the stop rib 19 with the right side of the bridge 12". Despite theability of the stop rib 19 to effect such stop action, the intermediatestrap 10 can be inserted beneath the bridge 12" from left to right asseen in FIG. 30 during initial assembly of the parts by effecting suchinsertion before the housing tube 6 is inserted over the spring 7,because, as will be seen in FIG. 30, the intermediate strap 10 is raisedby such tube to the extent of its thickness.

In FIG. 31 another modification of the limit latch is shown in which ametal strip 11', forming a bow spring 13d having a configurationdifferent from the hook 11 shown in FIGS. 5 to 22, has an end portionextending through transverse slots in an intermediate strap 10 generallyof the type shown in FIGS. 25 and 26.

A free end portion of the strip 11' can be depressed downward into aslot 11" extending lengthwise of the intermediate strap 10 to facilitatepassage of the bow spring 13d beneath the bridge 12" when strap 10 ismoved to the right as seen in FIG. 31. Movement of the intermediatestrap 10 to the right will be limited by abutment of the shoulder 15'with the left side of the bridge, and return movement of theintermediate strap from latched position of the latch will be preventedby the left side of the spring bow 13d engaging the right side of thebridge 12". The latch can be released by pushing the spring bow 13d backto the left of the crossbar of the bridge, which will also press thefree end of the strip 11' downward into the slot 11" of the intermediatestrap 10, so that such bow can pass beneath the bridge crossbar. Again,the normal operating range of movement of the intermediate strap 10relative to the force-producing unit 3 will be established between theposition shown in FIG. 31 and the position to the left at which the stoprib 19 is engaged with the right side of bridge 12".

Where the force exterted by the spring 7 in the various force-producingunits described above can be altered to provide the desired treatment,it is preferred that there be calibration means to indicate the degreeof force which is being produced by the spring in its different adjustedconditions. Such calibration means are shown in FIGS. 5, 8 and 21 to 27,as including a calibration scale 30 graduated in ounces, having linescorresponding to such graduations that are visible through thetransparent housing tube 6 for coordination with the end of the spring 7remote from the side strap 8. Thus in FIGS. 5 and 8 the spring 7 is setto provide an average working pull of sixteen ounces. In FIG. 21 thespring is set to provide an average working pull of eight ounces. InFIGS. 23 and 24 the spring is set to provide an average working pull ofthirty-two ounces.

Reference is made to the "average" working pull because considerablemovement of the side strap 8 relative to the force-producing unit 3occurs in the neckband type of appliance shown in FIG. 1 and the pull atone end of the working range will be different from the pull at theopposite end of the working range. Some range of movement is required tohook the tie rod 2 to the side strap 8. After such attachment, when thehead and lower jaw are held in the most usual position the right end ofthe spring 7 should be aligned with the zero index mark 31, as shown inFIG. 5. When the right end of the spring is aligned with such indexmark, the pull produced by the spring will be that designated by thecalibration line 30 aligned with the left end of the spring. When thespring moves to the left of the zero index mark 31 the pull of thespring will be somewhat reduced, as indicated by the minus signs at theindex 31. When the right end of the spring is pulled to the right beyondthe zero index mark, as indicated by the plus signs in FIG. 8, forexample, the pull produced by the spring will be greater than the lineof the calibrations 30 with which the left end of the spring is inregistration.

In any case the bridge 14, abutments 15 and stop rib 19 limit relativemovement of the intermediate strap 10 and the force-producing unit 3 inthe normal range of resilient movement to a distance less than theextent to which the spring anchor strap and the left end of the springcan be moved to alter the amount of average force produced by thespring. The operating range of the right end of the spring is usuallyfrom six to twelve millimeters and never over sixteen millimeters,whereas the left end of the spring should be adjustable over a range oftwelve to forty millimeters to provide a desirable range ofpredetermined forces to be applied to the tie rod 2.

In FIG. 32 a limit latch is combined directly with the side strap 8instead of an intermediate strap 10, and no disconnectible connection isprovided. The left end of the side strap 8 overlaps the right end of thebacking 5, and an enlargement 15" is provided on the left end of theside strap to which the right end of the spring 7 is connected directly.A stop rib 19' is provided on the backing 5, which is engageable by theleft end of the side strap 8 to limit relative contracting movement ofthe side strap and the backing 5 at the minimum pull end of the normalstroke. The maximum pull end of the normal stroke is reached when thelimit latch buttress tooth 13e comes into engagement with the left sideof the bridge 12, as discussed in connection with the operation of thelimit latch tooth 13b and the bridge 12" in the description of theappliance shown in FIGS. 25, 26 and 28.

In the form of the device shown in FIG. 32 a predetermined excessivepull applied to the tie rod 2 will move the buttress tooth 13e beneaththe bridge 12 to its right side, as shown. A ramp on enlargement 15"constituting a stop member will be engaged with the left side of thebridge 12 to prevent further extension movement of the side strap 8 andthe backing 5. The spring 7 will be immobilized when the parts havereached this condition. The buttress tooth 13e has clipped corners likethe corners of the tooth 13b shown in FIGS. 28 and 29. Consequently,when it is desired to release the limit latch, the side strap 8 can beswung relative to the backing in the manner indicated in FIG. 29, sothat the buttress tooth can move back to the left beneath the bridge 12.Initial assembly of the side strap 8 and the backing 5 can beaccomplished simply by threading the right end of the side strap beneaththe bridge 12 from left to right.

FIGS. 33, 34 and 35 show linear ratchet arrangements which can be usedto connect different components of the gear where it is desired to beable to establish different lengths of straps for different patients. InFIG. 33 such a linear ratchet arrangement is shown as being used toconnect the side strap 8 and an intermediate strap 10 of the type shownin FIGS. 25 and 26, while at the same time providing a connectiondisconnectible automatically in response to the occurrence of apredetermined excessive degree of pull. The linear ratchet includesbuttress teeth 32 molded integrally with the side strap 8. Thesebuttress teeth are of a height to snap successively beneath the bridge18 as the strap is pulled to the left relative to the intermediate strap10 in the direction indicated by the arrow.

When the desired length of strap 8 has been reached with an abrupt sideof a buttress tooth 32 engaging the left side of bridge 18, the end ofside strap 8 projecting to the left of the bridge 18 may be cut offappropriately so that the cut end will abut the stop rib 19 and leaveonly a single tooth at the left of the bridge. When the pull on the sidestrap 8 exceeds a predetermined value, the buttress tooth engaging theleft side of the bridge 18 will be pulled beneath the bridge todisconnect the connection between the intraoral component and theforce-producing unit in the manner described above.

In FIG. 34 the linear ratchet construction is shown as being used toconnect a tail strap 33 provided on the end of backing 5 remote from theside strap to an extraoral component reaction band member such as theheadcap 4. A stop rib 34 is provided on such headcap so that, when thetail strap has been threaded beneath a bridge 35 for a distancesufficient to provide the desired fit, the end of the tail strapprojecting beyond such bridge can be cut off appropriately to fitbetween the bridge and the stop rib and to leave only a single tooth atthe left of the bridge. Excessive pull beyond a predetermined value willdisconnect the connection afforded by the linear ratchet tooth 32engaging the left side of bridge 35.

Instead of providing the stop rib 19 as shown in FIG. 33, or the stoprib 34 as shown in FIG. 34, a suitable stop can be formed by providing asecond bridge 34' spaced to the left of bridge 18, as shown in FIG. 35.If this construction is used for tail strap 33, the second bridge 34'would replace the stop rib 34. With such a construction it would bedesirable for the bridge 34' to be made somewhat higher than the bridge18, so that the strap 8 could be pulled to the left to a desiredposition of adjustment more easily than it could be pulled to the rightto move a ratchet tooth under bridge 18. Again, when the desiredadjusted relationship between strap 8 and the bridge has beenestablished, the left end of the linear ratchet strap can be cut off sothat disconnection of the linear ratchet strap and the member carryingthe bridge can be accomplished by passage of a single buttress toothbeneath the bridge.

In FIGS. 36, 37 and 38 an alternative type of disconnectible connectionbetween the backing 5 and a head-engageable reaction component, such asthe headcap 4, is shown. By such connection headgear components ofdifferent size can be connected readily to the force-producing unit 3.In this instance the backing member has a short tail strap 33'insertible beneath the bridge 35 when moved in the direction indicatedby the arrow in FIG. 38. The backing 5 carries a bowed leaf spring 36,preferably of strip metal, which can be depressed either directlymanually, or by wedging action by pushing the left end portion of suchspring against the right side of bridge 35 as seen in FIGS. 36 and 38.Such bowed leaf spring will snap up at the left side of bridge 35 whenthe left end of the tail strap 33' has reached a position adjacent tothe stop rib 34, as shown in FIG. 36. If an excessive pull is exertedbetween the force-producing unit 3 and the headcap 4, the connectionbetween the tail strap 33' and the headcap will be disconnected as shownin FIG. 37 by yielding of the spring 36 in the manner described inconnection with spring 21, as shown in FIGS. 13 and 14.

In the type of appliance shown in FIGS. 39 to 45, inclusive, theadjacent end portions of the side strap 8 and the intermediate strap 10'overlap between parallel walls 37, connected by a bridge 38. The lowerportions of such walls have barbed projections 39 insertible throughslots 40 in the end portion of the backing 5 adjacent to the tie rod 2.The walls 37 will have sufficient resilience to enable their lower edgesto be moved toward each other so that the side barbs of the projections39 will snap beneath the backing 5 to hold the barbs securely inengagement with the underside of the backing 5.

The end of the housing tube 6 adjacent to the walls 37 has a top bevel,and a notch 41 in its lower side is engageable with a block 42projecting upward from the backing 5 to prevent rotation of the tuberelative to the backing. The end of intermediate strap 10' has across-rib 43 integral with it and the cross-rib side 44 facing thespring 7 is steeply inclined. Such rib side is engageable with thecomplementally inclined side 45 of cross-rib 46 on the adjacent end ofthe side strap 8.

A hook on the end of spring 7 is engaged in a hole in the adjacent endof intermediate strap 10', so that the spring tends to pull the strap tothe left as seen in FIGS. 40 to 43. In the absence of any opposing forcethe intermediate strap will be pulled into the position of FIG. 40 andheld in that position by engagement of the inclined side 44 of thecross-rib 43 with the right edge of a crossbar 47 connecting the twoupright walls 37. With the intermediate strap in this position, the endof side strap 8 remote from the cross-rib 46 can be threaded between thewalls 37, beneath the bridge 38 and above the cross-rib 43 of theintermediate strap 10' in the manner illustrated in FIG. 40.

As the cross-rib 46 of the side strap 8 moves between the walls 37, theinclined side 45 of the downwardly projecting cross-rib 46 will engagethe upper portion of the inclined side 44 of the cross-rib 43 onintermediate strap 10'. As the side strap 8 is pulled to the right, theengagement of its cross-rib side 45 with the cross-rib side 44 ofintermediate strap 10' will pull the intermediate strap to the right inopposition to the force exerted by spring 7 as indicated in FIG. 41. Thepressure between the inclined sides 45 and 44 will tend to wedge the endof side strap 8 carrying cross-rib 46 upward. Engagement of the upperside of such strap with the bridge 38 will limit such upward movement.

A top lug 48 projects upward from the upper side of the side strap 8adjacent to the cross-rib end of such side strap, which lug isengageable with the right edge of the bridge 38 when the side strap andthe intermediate strap 10' have been pulled to the position of FIG. 42.The wedging action produced by the engagement of the steeply inclinedside 44 of cross-rib 43 and the steeply inclined side 45 of cross-rib 46will snap the end of the side strap upward to the position of FIG. 42,so that the lug will engage the edge of the bridge if the pulling forceon the tie rod 2 to the right is relieved. Such engagement of the stoplug with the bridge edge will immobilize the spring 7 so that thecross-rib sides 44 and 45, the stop lug 48 and the bridge 38 constitutea limit latch operating in the manner described above for limit latchesof other forms of the present invention.

If the pulling force exerted on the tie rod 2 increases appreciablybeyond that required to pull the side strap 8 and the intermediate strap10' to the positions shown in FIG. 42, the straps will be moved into thepositions shown in FIG. 43 in which the end portion of the side strap 8clears the bridge 38, whereupon the wedging force between the steeplyinclined cross-rib sides 44 and 45 will cause the end of the side strap8 to be slid upward to the broken-line position shown in FIG. 43. Insuch position the side strap will be free from the intermediate strap toeffect disconnection of the disconnectible joint. When the cross-rib 43is thus freed from the pulling force on the side strap 8, the stress ofspring 7 will snap the intermediate strap back to the left from theposition of FIG. 43, so that the cross-rib 43 will engage the stop bar47, as shown in FIG. 40, but such snapback movement of the intermediatestrap will cause no difficulty because the intermediate strap issubstantially completely enclosed within the housing formed by thebacking 5, the sides 37 and the bridge 38.

In order to insure that the steeply inclined faces 44 and 45 of thecross-ribs 43 and 46 are retained reliably in engagement until the leftend of the side strap 8 has been drawn beyond the right edge of bridge38, it is desirable to provide rails 49 inclined from their endsadjacent to spring 7 outwardly away from the backing 5, which rails areintegral with such backing. The ends of such rails can be connected byan end wall 50 which projects from the backing 5 beyond the edges of therails to form a stop flange engageable by the end of intermediate strap10' when it has reached its limiting position to the right as seen inFIG. 43.

The parts of the appliance shown in FIG. 45 can be assembled by firstmounting the element including walls 37 and bridge 38 on the backing 5by pushing the barbed projections 39 through the slots 40. Theintermediate strap 10' can then be moved into the chamber between thewalls 37 lengthwise from right to left, as seen in FIGS. 40 to 43,inclusive. Next the hook of spring 7 can be engaged with thespring-anchoring aperture of the intermediate strap, and the housingtube 6 can be slid over the spring until its notch 41 is engaged withthe block 42. Finally the side strap 8 can be threaded between the walls37 and beneath bridge 38 from left to right, as stated above and shownin FIG. 40.

The spring 7 of the appliance shown in FIGS. 39 to 45 can be of thepreliminarily stressed type, or the initial stress of the spring can beadjustable by the arrangement shown in FIG. 39. The anchor strap 22connected to the left end of the spring 7 can be secured to the backing5 by a headed pin 51 extending through an aperture 23' in the springanchor strap 22 and through the backing 5. To maintain the tube 6 inproper lengthwise position, the left end of such tube may have a tabintegral with it interposed between the anchor strap and the backing,which is also apertured for penetration by the securing pin 51.

The degree to which the spring 7 is stressed, and consequently themagnitude of the pull exerted by the spring on the tie rod 2, can bealtered by shifting the spring anchor strap 22 lengthwise to engage theheaded pin 51 in different apertures 23' in the spring anchor strap. Thefarther to the left such strap projects, the greater will be the stressof the spring 7, and correspondingly greater will be the pull exerted onthe tie rod 2. The magnitude of the spring stress can be indicated bycalibrations 30 with which the end of the anchor strap 22 can bealigned. As discussed in connection with FIG. 5, for example, thecalibrations can be in increments of eight ounces, and the calibrationscan be located to cooperate with the end of the anchor strap 22 toindicate the stress of the spring.

Alternatively, the calibrations can be placed on the anchor strap itselfopposite the respective apertures, as shown in FIG. 39 and designated30'. While the calibrations on the right side of the spring anchor strapsignify ounces of average pull on the tie rod 2, such spring anchorstrap can be used with various springs having different loadcharacteristics. All helical tension springs, however, have a deflectionrate corresponding substantially linearly to the pull exerted by such aspring. Especially if the anchor strap 22 is to be used in associationwith springs having different characteristics, the spring loadadjustment apertures can simply be numbered 1, 2, 3, 4 and 5, asindicated along the left margin of the spring anchor strap in FIG. 39.

The calibrations at the left of FIG. 39 are stated to indicate averagevalues of pull on the tie rod 2. The calibrations are arranged todesignate the exact value of the pull on such tie rod when the stop lug48 on the side strap 8 is in registration with the zero index mark 31'on the bridge 38. When such stop lug is at the left of the zero indexmark, the pull exerted on the tie rod will be somewhat less than thevalue indicated by a calibration 30 or 30'. Conversely, when the stoplug is at the right of the zero index mark 31', the pull on the tie rodwill be somewhat greater than that indicated by a calibration 30 or 30'.

The force-producing unit 3, shown in FIGS. 46, 47 and 48, is similar tothat shown and described in connection with FIGS. 25 and 26. In thisinstance, however, the side strap 8' carries the member 13b of the limitlatch and is connected directly to spring 7. The opposite end of strap8' is connected to the tie rod 2e by a swivel connector 52. In thisinstance the tie rod is in the form of a J-hook. The shank of suchJ-hook extends under bridges 53 arranged in series on the backing 5.Such backing is secured to a neckband 1, and an auxiliary headband 4c isattached directly to the backing to extend upward across the head justforward of the ear to deter sagging of the side portion of the neckband.

FIG. 49 also shows a force-producing unit 3 similar to that shown anddescribed in connection with FIGS. 25 and 26, but in this instance thehousing tube 6' is made of comparatively rigid transparent plasticmaterial of preformed shape, so that it will maintain its shape withoutprovision of the tube-retaining band 29' shown in FIGS. 25 and 26despite the spring 7 housed within it being preliminarily stressed orbeing stressed to a considerable degree by lengthwise extension ofanchor strap 22.

The force-producing unit 3' shown in FIGS. 50 and 51 utilizes a helicalcompression spring for producing the force applied to the inraoralcomponent of the appliance instead of a helical tension spring as usedin the appliances shown in FIGS. 5 to 49, inclusive. In this unit thecompression spring 7' is received in housing tube 6', and its right endis seated on an internal flange at the right end of such tube. The sidestrap 8 has an extension 8" connected to a plunger rod 54 extendingaxially through the spring and carrying a plunger head 55 engageablewith the left end of spring 7'.

The backing 5' has a row of holes 56 extending lengthwise of it, whichhols are spaced apart corresponding to increments by which thecompression spring 7' could be contracted to alter the force which itproduces and which is applied to the side strap 8. The housing tube 6'has a tab projecting from its left end remote from its internallyflanged end on which the spring 7' seats. This tab has in it an aperturewhich can be placed in registration with various backing apertures 56 bymovement of the housing tube 6' lengthwise of the backing forcorrespondingly altering the length of the spring. The tube 6' can besecured to the backing 5' in any desired longitudinally adjustedposition by inserting the shank of a headed retaining pin 51 through theaperture in the tube tab and an aperture 56 of the backing 5' inregistration with the tab aperture.

In FIG. 50 calibrations 30" on the backing 5' are shown, designatingounces of pull exerted on the side strap 8. The average pull will beindicated by the calibration line in registration with the right end ofthe housing tube 6'. Such calibration will indicate the exact pull onthe side strap 8 when the plunger head 55 is in registration with thezero index mark 31'. If the side strap 8 has pulled the plunger head tothe right of such index mark, the pull on the side strap will becorrespondingly greater than the force indicated by the calibration inregistration with the right end of the tube 6', and if the side strap 8is to the left of the position in which it is seen in FIG. 50, so thatthe plunger head 55 is at the left of the zero index mark 31", the pullon the side strap 8 will be correspondingly less than the valueindicated by the calibration in registration with the right end of thetube 6'.

While the calibration lins 30" are shown in FIG. 50 as cooperating withthe right end of the housing tube 6', an additional or alternative typeof spring adjustment marking is shown by the numerals 1, 2, 3 and 4alongside the various apertures 56 of the row of apertures in thebacking 5'. Such digital calibrations can be utilized to indicate thevarious adjusted positions of compression springs 7' having differentspring characteristics.

Moreover, the compression spring 7' may be preliminarily stressed so asto produce a substantial force applied to the side strap 8, even whenthe pin 51 is securing the left end of the tube 6' to the aperturedesignated 1 of the backing 5'. In such case the extension of the spring7'is limited by engagement of the shoulder at the junction between theside strap 8 and its reduced portion 8" with the right side of thebridge 12 upstanding from the backing 5'. Such engagement of theshoulder with the bridge will establish one limit of the normal workingrange of the side strap, and the other limit of such range is reachedwhen the gradually inclined side of the buttress tooth 13b engages theleft side of the bridge 12. Further movement of the side strap 8 to theright will pull the buttress tooth beneath the bridge 12 to its rightside, effecting latching action of the limit latch formed by bridge 12and buttress tooth 13b in the manner described in connection with theappliance shown in FIGS. 25 and 26.

In the appliance of FIG. 52, the force applied by the force-producingunit 3" to the side strap 8 is produced by a flat spiral spring 7",received in a substantially flat casing or housing box 57 carried by theflat backing 5' in parallel relationship. The outer end portion of suchspring extends through a slot 58 in such housing and is connected to thereduced extension 8" of the side strap 8 which has a constructionsimilar to that shown in FIGS. 50 and 51. A tab projecting from the sideof such casing remote from the slot 58 has in it an aperture that can beplaced in registration with any selected one of the apertures 56arranged in a row lengthwise of the backing 5' to adjust the forceproduced by the spring 7' and applied to the side strap 8 through threduced extension 8".

The backing 5' may have calibrations 30" arranged alongside therespective apertures 56 to designate the force which would be producedby the spring 7' and applied to the side strap 8 corresponding to theadjusted position in which the pin 51 secures the casing tab to thebacking 5'. While the calibrations are shown as designating ounces offorce, the various apertures 56 could simply be designated by digits, asdiscussed in connection with the appliance shown in FIGS. 50 and 51. Theindex 31 also cooperates substantially with the end of the spring 7" ina manner similar to that described in connection with FIGS. 5 and 25 toindicate when the spring force being produced corresponds exactly to thecalibrations 30. The limit latch structure provided in this appliance isthe same as that shown in FIGS. 25, 26, 28, 29, 50 and 51 includingcooperating bridge 12 on backing 5' and buttress tooth 13b on strapextension 8".

The embodiment of the invention shown in FIGS. 53 to 58, inclusive, isgenerally similar to the embodiment shown in FIGS. 25 to 27, inclusive.The force-producing unit 3 includes the helical tension spring 7received in tube 6 carried by a backing 5.

In this instance the tube is restrained from lateral displacementrelative to the backing 5 by being lodged between posts 29' upstandingfrom the backing at opposite sides of the tube. The free ends of theposts are curved toward each other to restrain movement of the tube awayfrom the backing, but the posts are sufficiently flexible so that theirbent ends can be spread to enable the tube to be inserted between theposts by movement transversely of the length of the tube instead of itbeing necessary to move the tube lengthwise as required to assemble thetube beneath the arch 29' in the construction shown in FIGS. 25 and 26.

The intermediate strap 10 is shorter than such strap shown in FIGS. 25,26 and 27, because the modification of FIGS. 53 to 57 does not have anylimit latch including a buttress tooth 13b, but such limit latch couldbe provided in this embodiment of the invention if desired. As in theappliance shown in FIGS. 25, 26 and 27, movement of the intermediatestrap to the left is limited by engagement of stop rib 19 with the rightside of bridge 12".

A main feature of the modified structure shown in FIGS. 53 to 58 is thedisconnectible connection between the intermediate strap 10 and the sidestrap 8'. This connection has the same general type of structure as theconnection shown in FIGS. 25, 26 and 27 in including the bridge 18'spanning the end portion of the intermediate strap at the side of stoprib 19 remote from spring 7, which rib cooperates with a reversely-bentspring strip 20', 21' carried by the cooperating end of side strap 8'.The principal difference in the two structures is in the proportions ofthe parts and the manner in which they cooperate.

The structure of the connection shown in FIGS. 53 to 58, inclusive, isvery precise, enabling the minimum tension and the amount of movementbetween side strap 8' and intermediate strap 10 which will effectdisconnection of these strap members to be determined quite accurately.In order to be able to select most readily the predetermined minimumtension between strap 8' and strap 10 which will effect disconnection ofthe connection, it is preferred that the degree of such tension bedetermined almost entirely by the characteristics of the spring strip20', 21'. Consequently, bridge 18' with which such strip cooperates ismade of very rigid construction.

The bridge 18' has a deep arch as shown in FIG. 54, and its oppositeends are mounted on the widened end 17 of intermediate strap 10 byupwardly tapered walls 57 forming rigid connections to the intermediatestrap end. The rigidity of the widened end of the intermediate strap isalso increased by providing sidewalls 58 connecting the opposite ends ofthe stop rib 19 and the upwardly tapered walls 57 at the opposite endsof the bridge 18'.

The leaf spring 20', 21' shown by itself in FIG. 58 is arranged in theconnection to utilize both cantilever leaf spring characteristics anddsemielliptical leaf spring characteristics. The flat base 20' of thespring strip is inserted through a slit in the side strap 8', so thatsuch flat base portion of the spring underlies the underside of the endportion of side strap 8' while the bowed strip portion of the springlies alongside the other, i.e. upper, face of the side strap. The lengthof the widened portion 17 of the intermediate strap 10 is shown as beingapproximately equal to the combined lengths of the spring portions 20'and 21'.

The proportions of the connection parts and the spring characteristicsof the spring 20', 21' should be quite exact so as to provide a knownprestressed condition of the spring when the connector parts have beenassembled into the relationship shown in FIGS. 54 and 55. The side strap8' is assembled with the intermediate strap 10 in the manner describedin connection with FIGS. 25, 26 and 27, and illustrated particularly inFIG. 27. In such assembly operation the end of side strap 8' is threadedbeneath the bridge 18' and moved from left to right, as seen in FIG. 53,until the assembling operation is completed, with the parts in thepositions shown in FIGS. 54 and 55.

During movement of the side strap 8' in the direction indicated by thearrow in FIG. 53 relative to the intermediate strap 10, the bowedportion 21' will engage the bridge 18' before the tip of side strap 8'passes to the right beyond the stop rib 19. In order for the side strap8' to move relative to the intermediate strap 10 from the position ofFIG. 53 to the position of FIGS. 54 and 55, it may be necessary for thecantilever spring characteristics of the spring bow 21' to be overcomecompletely and such spring bow pressed downward until its free endengages the side strap.

If the side strap 8' is pulled to the right relative to the intermediatestrap 10 from the relative positions of these parts shown in FIG. 53,the bridge 18' will apply a wedging force to the right inclined side ofthe spring bow 21 for depressing such side so that the side strap cancontinue to be moved to the right. It is preferred that the left end ofthe cantilever bowed spring leaf 21' be engaged with the upper side ofthe side strap 8' before such side strap has been pulled far enough tomove its tip beyond the right side of the stop rib 19.

The additional movement required before the tip of side strap 8' willsnap past the right side of stop rib 19 into the position shown in FIG.55 should require that the arch of the bowed portion 21' of the springbe depressed to some extent. In such event the spring will beprestressed to the extent to the pull required to bend the bowed portionof the spring into contact with the side strap 8', if the spring is ofcantilever type, plus the pull required to depress the arch of the bowspring in order to enable the side strap to move relative to theintermediate strap sufficiently to accomplish such snap actionengagement of the parts. The parts will be maintained in such engagementas shown in FIG. 55 thereafter, even though the pull on the side strap8' is discontinued. Further movement of the side strap to the rightrelative to the intermediate strap can thereafter be effected only byexerting an extending pull on such straps exceeding the pull required tobe exerted in order to assemble the parts to the relationship shown inFIG. 55.

The amount of pull required to be exerted on side strap 8' to displacethe side strap relative to the intermediate strap should be greater thanthe pull exerted on the side strap 8' by spring 7 within the normalworking range of the appliance. Thus a pull which will stretch spring 7from the solid-line position of the intermediate strap 10 to thebroken-line position of that figure, in which the shoulder 15' isengaged with the left side of bridge 12", will be insufficient to effectrelative extension or separating movement of the side strap 8' andintermediate strap 10. If a pull is exerted on the side strap 8'sufficiently exceeding the pull required to assemble the side strap andthe intermediate strap in the relationship shown in FIG. 55 with thespring bow 21' prestressed, the spring bow can be wedged under thebridge 18' and the side strap can move farther to the right relative tothe intermediate strap 10, as shown in FIG. 56.

During such further movement of the side strap 8' to the right, theintermediate strap is restrained from being moved by the side strap 8'because of the engagement of shoulder 15' with the left side of bridge12", as shown in FIG. 56. When the arch of the spring bow 21' has beendepressed by wedging action of the bridge 18' to the position shown inFIG. 56, the side strap can be moved easily to the right from theposition of FIG. 56 to the position of FIG. 57, in which the side strap8' is disconnected from the intermediate strap 10.

The extension movement of side strap 8' relative to intermediate strap10 beyond the position of FIG. 55 to disconnect the straps is verysmall, such as three to seven millimeters. For the usual orthodontictreatment the pull exerted by spring 7 is in the range of eight toforty-eight ounces, that is, one-half a pound to three pounds. Thespring bow 21' may have a preload of four pounds when the parts are inthe position shown in FIG. 55, which means that a steady pull of fourpounds applied to the side strap 8' will not shift that strap to theright relative to the intermediate strap 10.

The spring 20', 21' may be selected so that a steady pull of five poundsapplied to the side strap 8' will move such side strap relative tointermediate strap 10 to and through the position of FIG. 56 todisconnect the connection. A sudden sharp pull of considerably lessmagnitude could also effect movement of the side strap 8' to the rightfrom the position of FIG. 55 to disconnect the side strap from theintermediate strap. The spring 20', 21' can be selected fordisconnection of the parts under loads of different magnitude dependingon the type of treatment for which the particular appliance is designed.

The apertures 9' in the side strap 8' of FIG. 54 are larger than theholes 9 in the side strap 8 of the appliance shown in FIGS. 25 to 27,for example, to facilitate connection of such side strap to the hook ofthe tie rod 2. Also such holes are shown as being numbered for recordpurposes in fitting the appliance to a particular patient.

I claim:
 1. In a selectable length connection for an orthodontic deviceincluding an elongated tension member having a plurality of ratchetteeth spaced along its length and an elongated bridge having its lengthextending transversely of the tension member for receiving the tensionmember therebeneath with a selected ratchet tooth engaging an edge ofthe bridge, the improvement comprising the tension member being movablegenerally lengthwise in both directions relative to the bridge, all ofthe rachet teeth being tapered in the same direction lengthwise of thetension member for movement beneath the bridge in one direction moreeasily than the teeth can move beneath the bridge in the oppositedirection, and the teeth and the bridge being formed cooperatively forpassage of such teeth beneath the bridge in said opposite direction whenthe pull on the tension member in said opposite direction exceeds apredetermined value.
 2. A resilient, stress-limiting safety connectioncomprising a tension member, a reaction member, and connecting meansconnecting said reaction member and said tension member and including aresilient force-producing unit connected to one of said members andnormally urging said tension member and said reaction member toward eachother but enabling relative movement of said tension member and saidreaction member away from each other into extended relationship, a firstelement connected to said resilient force-producing unit and a secondelement connectible with said first element and connected to the otherof said members for normally holding said members connected inopposition to force produced by said force-producing unit opposingmovement of said tension member and said reaction member away from eachother when in such extended relationship and tending to disconnect saidconnectible elements, said elements being disconnectible withoutstructural injury by exertion of pulling force between said tensionmember and said reaction member in opposition to the force urging saidtension member and said reaction member toward each other produced bysaid resilient force-producing unit exceeding a predetermined amountwhen said tension member and said reaction member are in extendedrelationship, said elements being again connectible to restore saidconnecting means to connected condition.
 3. A resilient, stress-limitingsafety connection comprising a tension member, a reaction member, andconnecting means connecting said reaction member and said tension memberand including a resilient force-producing unit connected to one of saidmembers and normally urging said tension member and said reaction membertoward each other but enabling relative movement of said tension memberand said reaction member away from each other into extendedrelationship, a first element connected to said resilientforce-producing unit and a second element connectible with said firstelement and connected to the other of said members for normally holdingsaid members connected in opposition to force produced by saidforce-producing unit opposing movement of said tension member and saidreaction member away from each other when in such extended relationshipand tending to disconnect said connectible elements, said elements beingdisconnectible without structural injury by movement of said tensionmember relative to said reaction member beyond such extendedrelationship, said elements being again connectible to restore saidconnecting means to connected condition.
 4. The connection defined inclaim 2, in which one of the elements is a spring element.
 5. Theconnection defined in claim 3, in which one of the elements is a springelement.
 6. The connection defined in claim 3, the resilientforce-producing unit including a helical spring.
 7. The connectiondefined in claim 6, the helical spring being a helical tension spring.8. The connection defined in claim 2, the resilient force-producing unitincluding a helical spring.
 9. The connection defined in claim 8, thehelical spring being a helical tension spring.
 10. An orthodonticappliance comprising extraoral force-reaction means engageable with thewearer's head and/or neck, orthodontic force-applying means for applyingforce to a jaw, and a spring force unit connecting said extraoralforce-reaction means and said force-applying means and including aspiral spring and adjusting means displaceable relative to one of saidmeans for altering the preliminary stress in said spiral spring toselect spring adjustments corresponding to average forces of differentpredetermined values.
 11. The appliance defined in claim 10, in whichthe force reaction means includes a flat backing, and the spring forceunit includes a substantially flat casing substantially enclosing thespiral spring and mounted on said flat backing in parallel relationship.12. The appliance defined in claim 11, in which the casing has anopening in one side for passage of a portion of the spiral springtherethrough and a tab projecting from its opposite side and overlyingthe flat backing, and anchoring means connecting said tab to the flatbacking.
 13. The appliance defined in claim 12, in which the anchoringmeans, for the purpose of anchoring the casing to the flat backing indifferent selected positions along the length of the flat backing,includes the flat backing having a plurality of apertures therein spacedalong its length and the tab carrying a projection engageable in anyselected one of such apertures.